SA Graan September 2017

September 2017

These differences in methylation were identified within dif-

ferent insect species and have shown to influence insect spe-

cialisation (for example the different roles/activities that different

bees in a hive perform) or the adaptation and virulence of insect

species.

Looking towards a brighter

research future

Being able to tell the difference between the Russian wheat aphid

biotypes quickly and effectively will enable scientists to spend

their time studying the ecology and life history of the different

biotypes. With this information, predictions could be made as to

which biotype(s) would be better adapted to which environmental

conditions, allowing breeders to pre-emptively develop resistant

cultivars.

In total 512 different primer combinations were tested with just a

handful showing differences between the four RWASA biotypes.

More primer combinations showed differences in RWASA2 and

RWASA4 biotypes, suggesting the presence of more methylation

pattern variation.

From years of phenotypic screening experience with RWASA

biotypes, this is an interesting result as RWASA2 and RWASA4

appear the more virulent and aggressive biotypes. RWASA3 and

RWASA1 were harder to differentiate.

In other insect species, methylation has been linked to virulence

changes. A few promising biomarkers that clearly identify each of

the four RWASA biotypes have been identified, namely primer pair

A (RWASA4), primer pair B (RWASA3), primer pair C (RWASA2) and

primer pair D (RWASA1). The red arrows in each photo (

Photo 3

Photo 6

) identify the unique biomarker for each RWASA biotype.

This is very encouraging because previously published SSR and

RAPD markers had been tested on the four RWASA biotypes without

successful differentiation. These international publications reported

on DNA based markers that could distinguish the specific Russian

wheat aphid biotypes that had been compared in those studies

but not necessary all Russian wheat aphid biotypes.

This methylation sensitive methodology might be the key to iden-

tifying biomarkers for all Russian wheat aphid biotypes around

the world and could possibly be a potential tool to identify or track

Russian wheat aphid biotype introductions.

Before publishing this data in a scientific journal, further evalua-

tion of these specific biomarkers will be done for the four RWASA

biotypes to validate their repeatability on both blind and mixed

biotype samples.

For further information, contact Drs Scott Sydenham

or Vicki Tolmay at 058 307 3400 or

sydenhams@arc

agric.za

1: A typical Russian wheat aphid family going for a walk.

2: Russian wheat aphid resistant cultivar versus a susceptible cultivar Russian wheat aphid damage in the field (1980s).

3: Primer pair A (RWASA4) – left (methylation sensitive) and right (methylation non-sensitive).

4: Primer pair B (RWASA3) – absent – left (methylation sensitive) and right (methylation non-sensitive).

5: Primer pair C (RWASA2) – left (methylation sensitive) and right (methylation non-sensitive).

6: Primer pair D (RWASA1) – left (methylation sensitive) and right (methylation non-sensitive).

Grain SA/Sasol photo competition